ABS (antilock brake system) prevents wheels from locking and comes into operation when a higher friction coefficient between a tire and the road is demanded than can be transmitted, i.e. when the driver brakes too hard. In the case of excessively hard braking, the central electronic control unit of the ABS brake system detects the tendency for one or more wheels to lock from rotational speed detector signals and, from these signals, calculates the activation of the pressure control valve arrangement acting on the associated brake cylinder. The brake pressure is then adjusted to an optimum slip of the pressure control valve arrangement, which lowers, holds or builds up the pressure in accordance with the wheel behavior and hence with the friction conditions between the tire(s) and the road.
ABS pressure control valve arrangements without a relay action, to which the exemplary embodiments and/or exemplary methods of the present invention relate, are used on vehicles such as commercial vehicles, buses, semitrailer trucks and trailers. Pressure control valve arrangements without a relay action generally have 3/2-way solenoid valves as pilot control valves for diaphragm valves, wherein an electronic control device activates the 3/2-way solenoid valves to enable the functions required for ABS operation, “pressure holding”, “pressure reduction” and “pressure buildup”, to be carried out. During a braking operation which does not involve a response by the ABS (no tendency for a wheel to lock), the pressure medium, generally air, flows through the pressure control valve arrangements unhindered in both directions during air admission to and venting from the brake cylinders. This ensures that the operation of the service brake system is not affected by the ABS pressure control valve arrangement.
Within the housing, pressure control valves of the type in question in the form of single-channel pressure control valves for antilock systems of motor vehicles have respective diaphragm valves as a holding valve and an outlet valve and respective solenoid control valves for the holding valve and the outlet valve. The two diaphragm valves each contain a diaphragm, which can be acted upon by the pressure in a control chamber, wherein the control chamber is closed off from the outside by a cover secured on the housing.
A pressure control valve arrangement of the type in question for an ABS brake system is known from EP 0 266 555 A1, for example. In the prior-art pressure control valve arrangements, the two diaphragm valves are generally arranged on the side of the housing, wherein the corresponding pilot control spaces are closed off by covers secured on the side of the housing. These covers are produced by primary forming processes such as injection molding. Pressure medium channels are furthermore formed in the housing in order to carry pressure medium within the housing to and from the various connections of the pressure control valve arrangement and to and from the diaphragm valves and to and from the solenoid valves controlling the above valves.
The pressure medium channels may run in a vertical and/or horizontal direction within the housing because then the housing does not have to be re-clamped during the machining of the pressure medium channels of a machining center, for example. A change in the direction of such a pressure medium channel is problematic in terms of flow engineering because the deflection of the flow in the pressure medium channel concerned is then generally 90 degrees (deflection from the vertical to the horizontal or vice versa) and this results in relatively high flow losses due to the abrupt deflection in such a pressure medium channel elbow. However, because a high dynamic response is required in pressure control valve arrangements for ABS/ASR systems and as rapid as possible venting of the brake cylinder concerned is required, for example, in the context of the “pressure lowering” function when the permissible wheel slip is exceeded, such flow losses caused by deflections must be kept as small as possible.
Because the installation dimensions of such a pressure control valve arrangement, especially the installation width thereof, are standardized and invariable owing to restricted space conditions, a solution to this problem cannot consist in enlarging the flow cross sections of the pressure medium channels.
Given this situation, it is the underlying object of the invention to develop a pressure control valve arrangement of the type mentioned at the outset in such a way that the flow losses or flow resistance, especially in pressure medium channels deflecting a pressure medium flow, are reduced. At the same time, the outlay on the production and finishing of the manner for achieving this object should be as low as possible.